Amplifiers – With periodic switching input-output
Patent
1985-04-12
1986-06-10
LaRoche, Eugene R.
Amplifiers
With periodic switching input-output
330 51, 330263, H03F 114, H03F 326
Patent
active
045945586
ABSTRACT:
A driver-sensor circuit for a circuit-testing device has a sensor amplifier (Q1, Q2, Q3, and Q4) for sensing the voltage on a device under test connected to its input-output terminal (12). The driver-sensor circuit also includes a driver amplifier (Q5, Q6, Q7, and Q8) for driving the same terminal (12). The driver amplifier (Q5, Q6, Q7, and Q8) can be switched on and off, and a limiting amplifier (Q9, Q10, Q11, and Q12) applies the sensor-amplifier output voltage to the input terminal (20) of the driver circuit (Q5, Q6, Q7, and Q8) to keep the reverse bias on the driver-amplifier transistors (Q5, Q6, Q7, and Q8) to a minimum. To eliminate offset bias current at the input terminal 12 of the sense amplifier (Q1, Q2, Q3, and Q4), compensation transistors (Q15, Q16 ) matching the input-stage transistors (Q1, Q2) of the driver amplifier have their bases tied together to force their base currents to cancel. The resultant emitter currents of the compensation transistors (Q15, Q16) are sensed by amplifiers (52, 54) that control the emitter currents of the first-stage transistors (Q1 and Q2) so that their emitter currents are the same as the emitter currents of the compensation transistors (Q15, Q16). In this way, the base currents of the first-stage transistors (Q1, Q2) are forced to be opposite and thus cancel.
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GenRad Inc.
LaRoche Eugene R.
Mottola Steven J.
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